1. Field of the Invention
The present invention relates to a hydraulic control valve adapted for use in a construction machine such as a power shovel.
2. Description of Prior Art
A conventional power shovel comprises, as illustrated in FIG. 9, a lower self-propelled movable body 1 driven by a propelling motor, not shown, an upper turntable 2 capable of being turned by a turning motor, not shown, and a working machine 3 mounted at the front portion of the turntable 2.
The working machine 3 has a boom 6 which can be swung rightward and leftward by a swinging cylinder 4 and movable vertically at the tip end thereof by a boom cylinder 5 and an arm 8 pivotally mounted at the tip end of the boom 6 which is turned by an arm cylinder 7.
The arm 8 has a tip end to which a bucket 10 is attached so as to be turned by a bucket cylinder 9. A blade 12 which is vertically movable by a blade cylinder 11 is mounted at the front portion of the movable body 1.
A hydraulic control valve 13 provided at each actuator controls the propelling motor, the turning motor and hydraulic actuators composed of various cylinders. Each hydraulic control valve 13 is, as illustrated in FIG. 10, normally connected with one another.
Each hydraulic control valve 13 comprises, as illustrated in FIG. 11 , a valve body 13a, a spool 14 housed in the valve body 13a for switching oil passages in the valve body 13a, the spool 14 normally being retained at a neutral position by a return spring 13b wherein an oil under pressure supplied to a pump port 13c is drained through a drain port 13d into a tank 16 by way of a port block 15.
The valve body 13a of the hydraulic control valve 13 is, as illustrated in FIG. 12, conventionally formed integrally by casting. However, in the conventional hydraulic control valve 13, a main core for forming a spool port 13h is complex so that narrow passages can not be formed in the hydraulic control valve 13 since a cylinder drain port 13e, a bridge port 13g and the spool port 13h are separately formed in three stages. As a result, this was an obstacle to making the hydraulic control valve compact in size since the diameter of the spool port 13h could not be less than that ranging from 11 mm to 12 mm.
The present invention has been made in view of the problem set forth above and is to provide a hydraulic control valve so that a valve body can be manufactured without using cores having complex structures.
Particularly, the conventional control valve body is, as described above, integrally formed by casting and a passage of a neutral port in a valve chamber is also formed by casting wherein cores are employed for forming the passage of the neutral port at the time of casting. The core is formed, as illustrated in FIG. 13, by casting a main core 19 for forming the spool port 13h and thereafter by jointing joint cores 20 and 21 to the main core 19. There was a problem in that a mold can not be split along the line X--X when forming the core if the jointing cores 20 and 21 are integrated with each other, which involves the following drawbacks.
(1) A jointing operation of the cores is manually made which results in preventing an automatic assembly of the cores, hence this is inefficient.
(2) Jointing deviation between the cores is liable to occur which involves a deteriorated casting accuracy.
(3) Casting flash is liable to occur at the jointing portions of the cores.
(4) Jointing agent causes generating gas at the time of casting which is likely to generate a casting porosity.
Accordingly, it is a second object of the present invention to provide a hydraulic control valve capable of manufacturing a valve body by machining the passage without using the conventional jointing cores, whereas the passage was conventionally formed by the jointing cores.
The valve body 13a of the conventional control valve 13 forms therein, as illustrated in FIG. 14, a parallel port 13f, the bridge ports 13g, cylinder ports 13i and the cylinder drain port 13e wherein a load check valve 17 for allowing the oil under pressure only to flow from the parallel port 13f into the bridge port 13g is provided between the parallel port 13f and the bridge port 13g and a hydraulic cylinder 18 is connected to the cylinder ports 13i therebetween.
If the spool 14 of the control valve 13 having the arrangement set forth above is moved rightward, the oil under pressure introduced into the pump port 13c reaches the parallel port 13f and pushes the load check valve 17, then flows into the bridge ports 13g. The oil under pressure is further introduced into a bottom side of a hydraulic cylinder 18 from cylinder ports 13i which communicates with the spool 14 by the movement of the spool 14 so as to stretch the hydraulic cylinder 18 whereas the oil under pressure at the side of the cylinder rod flows from the cylinder ports 13i to the cylinder drain port 13e and thereafter drained into a tank 16.
During the operations set forth above, if a shock is applied to the hydraulic cylinder 18 or a tensile force acts on the hydraulic cylinder 18 for some reasons, an anomalous pressure or a negative pressure is generated in the hydraulic circuit which causes the hydraulic cylinder 18 to be damaged or unstable. As a result, this is likely to cause an obstruction for working.
To prevent such a problem, a suction salty valve 120 is conventionally provided, as illustrated in FIG. 15, between the cylinder ports 13i and the cylinder drain port 13e for preventing the anomalous pressure or the negative pressure from being generated.
That is, when the anomalous pressure is generated in the cylinder ports 13i, a poppet 121 provided inside the suction safty valve 120 is released so that the pressure inside the cylinder ports 13i is relieved into the cylinder drain port 13e to prevent the anomalous pressure from being generated in the hydraulic circuit.
When the negative pressure is generated in the cylinder port 13i, a suction valve 122 is released by the negative pressure so that the oil under pressure in the tank 16 is introduced into the cylinder port 13i from the cylinder drain port 13e whereby the negative pressure is prevented from being generated in the hydraulic circuit.
Inasmuch as the conventional hydraulic control valve 13 has the suction safety valve 120 serving as the safty valve function and the suction valve function combined in a single valve so that the structure of the valve is complex which impedes the miniaturization thereof.